Landfill capping system

The regulations for landfill basal liners and landfill capping systems, a field of special interest for HDPE geomembrane application and of exem-... 

Stormont, J.C., Incorporating capillary barriers in surface cover systems, Environmental Science and Research Foundation, Proceedings, Landfill Capping in the Semi-Arid West Problems, Perspectives, and Solution, Grand Teton National Park, WY, ESRF-019, May 21-22, 1997, pp. 39-51. 

This section describes the elements in a closure or cap system of a completed landfill, including flexible membrane caps (FMCs), SWCR systems, gas control layers, biotic barriers, and vegetative top covers. It also discusses infiltration, erosion control, and long-term aesthetic concerns associated with securing a completed landfill. 

Phytoremediation is the use of plants to treat or stabilize contaminated soils, sediments, or water. Plants provide and support remediation processes in many ways. Common applications of phytoremediation-based systems include remediation of contaminated soil and groundwater, reuse of municipal wastewater and biosolids, reuse of industrial wastewater and by-products, alternative landfill capping and erosion control, and landfill leachate reuse. 

As an alternative to conventional landfill caps, Ecolotree caps offer low-maintenance systems with long-term durability. They are often significantly less expensive than conventional landfill caps. In addition, public acceptance of the technology can be very high, in part because of the parkUke aesthetic that provides bird and wildlife habitat. 

The area of woodlands cleared. Efficient use of the landfill area should be maximized. The amount of initial excavation will be minimized because, while one cell is being filled with waste, the next cell in sequence is being partially excavated. When the current working portion is completed, the liner system should be extended over the newly excavated cells. Once the new cells become the active cells, the cap system will be extended over the completed cells. 

HDPE geomembranes can be combined with various other components (leak monitoring system, geosynthetic clay liners of high durability, polymer amended sand-bentonite-mixtures, capillary barriers) to form alternative composite liners as reliable and cost effective capping systems (Simon and Muller 2004). Such alternative capping systems are tested and increasingly applied for landfills and for the containment of contaminated sites. 

Figure 1 illustrates the components of municipal solid waste (MSW) landfill waste containment systems. MSW landfills are by far the most common type of engineered waste containment system, followed (with respect to frequency of occurrence) by cover systems (caps) for uncontrolled dumps and hazardous waste sites and then by hazardous waste landfills. Caps and containment systems for hazardous waste landfills employ similar elements to MSW landfills. The performance of ancillary facilities at a waste disposal site subject to seismic loading, including leachate and gas treatment facilities, surface water control systems, access roadways, and landfill monitoring systems, is also an important consideration but will not be addressed herein. 

At the Lipari Landfill site in New Jersey, the gas venting system installed in 1983 consisted of two underground 4-inch (10-cm) perforated PVC pipes and five vent risers. Two parallel PVC pipes were installed 200 feet apart prior to cap emplacement during the period of wall construction and were placed about 3 feet beneath the finished grade. The vent risers were connected to the buried manifold pipes and consisted of open pipe installed perpendicular to the underground pipes and the ground surface. Filters were not attached to the riser exit points (U.S. EPA, 1987). 

Figure 26.31 shows a typical landfill profile designed to meet U.S. EPA s MTG requirements.38 The upper subprofile comprises the cap, or cover, and includes the required 2-ft vegetative top cover, 1-ft lateral drainage layer, and low-permeability cap of barrier soil (clay), which must be more than 2 ft thick. This three-tier system also includes an optional FMC and an optional gas control layer. The guidance requires a 40-mil thick FMC. 

Gas-collector systems are installed directly beneath the low-permeability clay cap in a hazardous waste landfill. Landfills dedicated to receiving only hazardous wastes are relatively new and gas has never been detected in these systems. It may take 40 years or more for gas to develop in a closed secure hazardous waste landfill facility. Because the long-term effects of gas generation are not known, and costs are minimal, U.S. EPA strongly recommends the use of gas-collector systems. 

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